Stabilizers for polymers containing aliphatically-bound bromine

ABSTRACT

Aliphatic bromine-containing polymers are stabilized using a mixture of an alkyl phosphite and an epoxy compound. This stabilizer package is very effective at preventing cross-linking reactions from occurring when the aliphatic bromine-containing polymer is subjected to high temperatures as are seen in melt processing operations. The stabilized aliphatic bromine-containing polymer is useful as a flame retardant for other polymers, notably polystyrene foam.

This application claims priority from U.S. Provisional Application No.61/138,572, filed 18 Dec. 2008.

The present invention relates to stabilized compositions that contain abrominated polymeric flame retardant.

Hexabromocyclododecane, a commonly used flame retardant for polystyrenefoams, is facing regulatory pressure in various jurisdictions, in partbecause it is thought to bioaccumulate. Therefore, there is a desire toreplace it.

Certain brominated polymers are promising candidates for replacinghexabromocyclododecane as a flame retardant in various polymer systems.These materials have molecular weights high enough that they are notexpected to bioaccumulate. Various polymers that contain aliphaticcarbon-carbon unsaturation can be brominated to high bromine contents,and the high bromine content makes them efficient as FR additives.Brominated polymers often possess other key characteristics, too,including compatibility with other polymers and other additives (notablyfoaming agents). In this respect, the brominated polymers arepotentially versatile FR additives, as the polymer backbone can beselected or tailored for use with specific bulk resins. For example,polystyrene blocks can be included in a brominated butadiene polymer toimprove dispersibility into a polystyrene resin. In polymer foamapplications, the FR additive should not have a significant adverseeffect on the foaming process or on the produced foam, particularly onfoam cell formation and foam cell size.

The performance of brominated FR additives depends to a large extent onthe thermal stability of the bromine-carbon bonds. These bonds must bestable enough to endure the heat conditions encountered during thevarious melt-processing operations that may be used, for example, toincorporate the FR additive into a bulk resin or to process theresulting blend into a useful article. The FR additive may be exposed totemperatures of 230 to 250° C. or even higher during these processingoperations, and should not release a significant amount of the bromineunder these conditions. At somewhat higher temperatures, typically from300 to 400° C., the FR additive must thermally degrade to produce anactive bromine-containing species which is understood to help suppressflames under fire conditions.

If a brominated FR additive is not thermally stable enough, bromine canbecome liberated during melt processing. This can cause severalproblems. One problem is that the loss of bromine during processing canlead to a loss of FR performance and to degradation of the bulk polymerthat contains the brominated FR additive. Another problem is that thelost bromine can form HBr, which is an acid that can corrode processingequipment, further catalytically degrade the FR additive and presentconcerns about worker exposure.

A third problem has been discovered to exist when the brominated FRadditive is a high molecular weight polymer. Loss of bromine can lead tothe formation of intermolecular bonds between polymer chains. Onepossible mechanism involves the formation of aliphatic carbon-carbonunsaturation in the polymer. This unsaturation is polymerizable. Underconditions of high temperature, these unsaturated species, as well asother residual unsaturation that may be present in the polymer, cancouple with other polymer molecules to form materials that have an evenhigher molecular weight. Because the molecular weight of the brominatedpolymer is high to begin with, it is not difficult to build enoughmolecular weight and/or crosslinking to form insoluble gels.

Gels can cause cosmetic imperfections in the product and in some casescan affect its performance. The gels can build up on the interiorsurfaces of the processing equipment. A special problem can occur inmaking foamed materials. The gelled material can interfere with theformation of the cell structure of the foam and also can have adverseaffects on its physical properties. This is because the viscoelasticproperties of the gelled material often are significantly different thanthose of the FR additive by itself.

The extent of gelling is dependent on time and on process temperatures.The amount of gelling can become quite significant, especially if thematerial is melt processed at temperatures above 200° C. This problem isparticularly acute in thermoplastic foam extrusion processes and otherprocesses which generate a large amount of scrap. To reduce costs, thescrap is recycled back into the process. Gelled materials and FRadditive contained in the scrap are therefore recycled as well. The gelsoften cannot re-melt when recycled back in this way. The recycled gelledmaterials and the FR additive are subjected to additional exposure tohigh processing temperatures. This can lead to accelerated gelformation, as the gel particles may participate in additional reactions.As a result, the gelled material accumulates in the product as more andmore of the scrap is recycled. It is very important to reduce this gelformation as much as possible.

Therefore, it would be desirable to provide a way in which to reduce orprevent gelling of aliphatic bromine-containing polymers and copolymerswhen they are exposed to elevated temperatures. This should beaccomplished at low cost, using materials or methods which do not havesignificant adverse impact on the melt processing operation itself orthe resulting product. When the product of the melt processing operationis a foamed material, the foam structure, i.e., cell size, cell sizedistribution and open/closed cell content should be at most minimallyaffected.

The present invention is in one aspect a process for producing a polymercomposition, comprising melt processing a mixture containing a moltenbulk polymer and an aliphatic bromine-containing polymer in the presenceof (1) at least one alkyl phosphite, (2) at least one epoxy compound, or(3) both (1) and (2).

Alkyl phosphite and epoxy compounds each have been found tosignificantly reduce the formation of gels in the melt processingoperation. In addition, these materials also improve the thermalstability of the aliphatic bromine-containing polymer, as determinedaccording to a weight loss test as described below. The alkyl phosphiteand epoxy compounds are effective at small addition levels, and so addlittle cost and have minimal effect on the melt processing operation orthe properties of the melt-processed polymer. In the preferred processin which the melt processing operation is an extrusion foaming process,the presence of the alkyl phosphite compounds and epoxy compounds haslittle adverse effect on cell size and foam physical properties.

Another advantage of the invention is that the amount of epoxy compoundthat is needed is usually small, minimizing cost, potential adverseeffects on flammability properties and potential build up of lowermolecular weight materials on interior and exterior surfaces ofprocessing equipment. Similarly, the presence of other stabilizers, suchas various inorganic materials, polyhydroxyl compound and organotinstabilizers, can be eliminated or minimized. Therefore, adverse effectsthat are sometimes seen when these materials are used, particularlyadverse effects on foam cell structure, can be avoided or reduced.

These effects are more pronounced when at least one alkyl phosphite andat least one epoxy compound are used in combination. The combination ofthese compounds has an additional benefit of permitting the amount ofepoxy compound that is required to obtain a given level of performanceto be reduced. This is desirable from a cost standpoint, and also tominimize the use of additives which may effect processing equipment.These effects are reduced if the addition level is smaller.

The reduced gel formation provided by the invention permits scrap to berecycled into the melt processing operation more readily, as gels areless apt to build up in the system. The reduced gel formation canprovide cosmetic benefits, and in some cases can have a beneficialeffect on the properties of the finished product.

In another aspect, this invention is also a polymer compositioncomprising (a) a bulk polymer, (b) an aliphatic bromine-containingpolymer, and (c) at least one alkyl phosphite, at least one epoxycompound or a mixture of at least one alkyl phosphite and at least oneepoxy compound, and is in still another aspect a composition comprisingan aliphatic bromine-containing polymer, and at least one alkylphosphite, at least one epoxy compound or a mixture of at least onealkyl phosphite and at least one epoxy compound.

In this invention, a bulk polymer is melt processed in the presence ofan aliphatic bromine-containing polymer, an alkyl phosphite and/or anepoxy compound. The bulk polymer can be any thermoplastic polymer whichis capable of being melt-processed at a temperature of 250° C. or below.The bulk polymer and the aliphatic bromine-containing polymer should beselected together so that the aliphatic bromine-containing polymer iscompatible with the molten bulk polymer. An aliphatic bromine-containingpolymer is considered to be compatable with the bulk polymer forpurposes of this invention if it is miscible in the bulk polymer at therelative proportions that are present, or if it can be dispersed withinthe bulk polymer to form finely dispersed domains. These domainspreferably are mainly less than 25 microns and more preferably less than10 microns in size, although some larger domains may be present. Theformation of mainly macroscopic (˜100 micron or greater in scale)domains of the aliphatic bromine-containing polymer in themelt-processed product indicates such a lack of compatibility.

Thermoplastic polymers of interest as the bulk polymer include vinylaromatic polymers (including vinyl aromatic homopolymers, vinyl aromaticcopolymers, or blends of one or more vinyl aromatic homopolymers and/orvinyl aromatic copolymers), as well as other organic polymers in whichthe aliphatic bromine-containing polymer is soluble or can be dispersedto form domains of predominantly less than 25 μm, preferably less than10 μm, in size. Polymers and copolymers of styrene are preferred. Mostpreferred are polystyrene homopolymers, and copolymers of styrene withethylene, propylene, acrylic acid, maleic anhydride, and/oracrylonitrile. Polystyrene homopolymer is most preferred. Blends of anytwo or more of the foregoing polymers, or of one or more of theforegoing polymers with another resin, also can be used as the bulkpolymer.

The bulk polymer should have a molecular weight high enough to allow formelt processing. Generally, a number average molecular weight of atleast 10,000. For purposes of this invention, molecular weights of thebulk polymer and the aliphatic bromine-containing polymer are apparentmolecular weights as measured by Gel Permeation Chromatography (GPC),relative to a polystyrene standard. GPC molecular weight determinationscan be performed using an Agilent 1100 series liquid chromatographequipped with two Polymer Laboratories PLgel 5 micrometer Mixed-Ccolumns connected in series and an Agilent G1362A refractive indexdetector, or equivalent device with tetrahydrofuran (THF) or othersuitable solvent flowing at a rate of 1 mL/min and heated to atemperature of 35° C. as the eluent.

The aliphatic bromine-containing polymer is an organic polymer thatcontains bromine atoms bonded to aliphatic carbon atoms. The aliphaticbromine-containing polymer preferably has little or no bromination onany aromatic rings that may be present. Even more preferably, thealiphatic bromine-containing polymer has little or no bromination atallylic or tertiary carbon atoms, contains few or no sites ofhydrobromination (i.e. sites at which bromine and hydroxyl groups appearon adjacent carbon atoms). The presence of significant amounts of thesegroups tends to reduce the thermal stability of the aliphaticbromine-containing polymer.

The aliphatic bromine-containing polymer is conveniently prepared bybrominating a starting polymer that contains sites of aliphatic,non-conjugated carbon-carbon unsaturation. The bromination reaction addsbromine across some or all of these unsaturation sites, binding bromineatoms to aliphatic carbon atoms and thereby producing the aliphaticbromine-containing polymer. The starting polymer preferably containsenough of those unsaturation sites such that, upon bromination, theresulting aliphatic bromine-containing polymer contains at least 20%,preferably at least 35% by weight bromine. The bromine content may be ashigh as 60%, 65%, 70% or more.

The starting polymer suitably has a weight average molecular weight (Mw)within a range of from 1,000 to 400,000, preferably from 2,000 to300,000, more preferably from 5,000 to 200,000 and even more preferablyfrom 20,000 to 200,000.

Examples of suitable starting polymers include (i) homopolymers andcopolymers of a conjugated diene such as butadiene, isoprene or a1,3-cycloaliphatic diene; (ii) a polymer or copolymer of allylmaleimide,especially a copolymer thereof with styrene; (iii) an aliphaticallyunsaturated polyester; (iv) an allyl ether of a novolac resin, (v) aROMP polymer or copolymer or (vi) a poly(4-vinyl phenol allyl ether).Some of these starting polymers are described in WO 2007/019120.

Preferred among the type (i) starting polymers are homopolymers orcopolymers of butadiene. Preferred among these are copolymers ofbutadiene and at least one vinyl aromatic monomer. Such a copolymer maybe a random, block or graft copolymer. A “vinyl aromatic” monomer is anaromatic compound having a polymerizable ethylenically unsaturated groupbonded directly to a carbon atom of an aromatic ring. Vinyl aromaticmonomers include unsubstituted materials such as styrene and vinylnaphthalene, as well as compounds that are substituted on theethylenically unsaturated group (such as, for examplealpha-methylstyrene), and/or are ring-substituted. Ring-substitutedvinyl aromatic monomers include those having halogen, alkoxyl, nitro orunsubstituted or substituted alkyl groups bonded directly to a carbonatom of an aromatic ring. Examples of such ring-substituted vinylaromatic monomers include 2- or 4-bromostyrene, 2- or 4-chlorostyrene,2- or 4-methoxystyrene, 2- or 4-nitrostyrene, 2- or 4-methylstyrene and2,4-dimethylstyrene. Preferred vinyl aromatic monomers are styrene,alpha-methyl styrene, para-methyl styrene, and mixtures thereof.

A useful starting butadiene polymer contains at least 10% by weight ofpolymerized butadiene. Butadiene polymerizes to form two types ofrepeating units. One type, referred to herein as “1,2-butadiene units”takes the form

and so introduce pendant unsaturated groups to the polymer. The secondtype, referred to herein as “1,4-butadiene” units, takes the form—CH₂—CH═CH—CH₂— and introduce unsaturation into the main polymer chain.A starting butadiene polymer preferably contains at least some1,2-butadiene units. Of the butadiene units in the starting butadienepolymer, at least 10%, preferably at least 15% and more preferably atleast 20% and even more preferably at least 25% are 1,2-butadiene units.1,2-butadiene units may constitute at least 50%, at least 55%, at least60% or at least 70% of the butadiene units in the starting butadienepolymer. The proportion of 1,2-butadiene units may be in excess of 85%or even in excess of 90% of the butadiene units in the starting polymer.

Methods for preparing butadiene polymers with controlled 1,2-butadienecontent are described by J. F. Henderson and M. Szwarc in Journal ofPolymer Science (D, Macromolecular Review), Volume 3, page 317 (1968),Y. Tanaka, Y. Takeuchi, M. Kobayashi and H. Tadokoro in J. Polym. Sci.A-2, 9, 43-57 (1971), J. Zymona, E. Santte and H. Harwood inMacromolecules, 6, 129-133 (1973), and H. Ashitaka, et al., in J. Polym.Sci., Polym. Chem., 21, 1853-1860 (1983).

Styrene/butadiene copolymers are especially preferred, particularly whenthe bulk polymer is a styrene homopolymer or copolymer.Styrene/butadiene block copolymers that are useful as the startingpolymer include those available from Dexco Polymers under the tradedesignation VECTOR™ are suitable. Styrene/butadiene random copolymersmay be prepared in accordance with the processes described by A. F.Halasa in Polymer, Volume 46, page 4166 (2005). Styrene/butadiene graftcopolymers may be prepared in accordance with methods described by A. F.Halasa in Journal of Polymer Science (Polymer Chemistry Edition), Volume14, page 497 (1976). Styrene/butadiene random and graft copolymers mayalso be prepared in accordance with methods described by Hsieh and Quirkin chapter 9 of Anionic Polymerization Principles and PracticalApplications, Marcel Dekker, Inc., New York, 1996.

A starting butadiene polymer may also contain repeating units formed bypolymerizing monomers other than butadiene and a vinyl aromatic monomer.Such other monomers include olefins such as ethylene and propylene,acrylate or acrylic monomers such as methyl methacrylate, methylacrylate, acrylic acid, and the like. These monomers may be randomlypolymerized with the vinyl aromatic monomer and/or butadiene, may bepolymerized to form blocks, or may be grafted onto the startingbutadiene copolymer.

The most preferred type of starting butadiene polymer is a blockcopolymer containing one or more polystyrene blocks and one or morepolybutadiene blocks. Among these, diblock and triblock copolymers areespecially preferred.

Starting polymer type ii) materials include copolymers of styrene andallylmaleimide. Polymers of this type can be represented by theidealized structure:

wherein x and y represent the mole fraction of the respective repeatingunits. In the foregoing structure, some or all of the respective styreneand allylmaleimide repeating units can alternate, and some or all of therespective styrene and 2,3-dibromopropylmaleimide repeating units canform blocks of two or more consecutive units of the same type. The moleratio of styrene to allyl maleimide repeating units in the startingcopolymer can range from 95:5 to about 40:60, but allyl maleimide levelstowards the high end of this range (such as from 30 to 60 mole percentmaleic anhydride) are preferred as this permits a higher bromine contentto be obtained in the final product. This type of copolymer isconveniently made from a styrene-maleic anhydride copolymer. Reaction ofthe styrene-maleic acid copolymer with allylamine converts maleicanhydride repeating units to N-allylmaleimide repeating units. Afterbromination, at least a portion of the allyl maleimide repeating unitsare brominated to provide a brominated polymer having the structure:

wherein x and y are as before.

Aliphatic polyesters that are useful starting unsaturated polymersinclude those having an -A-B- structure, in which A represents adicarboxylic acid repeating unit and B represents a diol repeating unit.Some or all of the A and/or B units contain, prior to bromination,non-aromatic carbon-carbon unsaturation. Polyesters of this type can beprepared in a reaction of a dicarboxylic acid (or corresponding acidhalide or anhydride) with a diol, at least one of which containsnon-aromatic carbon-carbon unsaturation. Examples of dicarboxylic acidsand corresponding anhydrides having non-aromatic carbon-carbonunsaturation include maleic acid, maleic anhydride, fumaric acid,fumaric anhydride, tetrahydrophthalic acid, tetrahydrophthalicanhydride, i.e.,

and the like. Those diacids or anhydrides and/or their respective acidhalides can be used to prepare a starting polyester that has A unitswith non-aromatic carbon-carbon unsaturation. 1,4-Dihydroxy-but-2-ene isan example of a diol having non-aromatic carbon-carbon unsaturation, andcan be used to make a starting copolymer having B units that havecorresponding unsaturation. Specific types of unsaturated polyestersthat are useful as starting polymers include, for example, polyesters ofmaleic acid or a maleic acid/fumaric acid mixture, optionally one ormore additional diacids, and one or more aliphatic diols; polyesters oftetrahydrophthalic anhydride with one or more aliphatic diols;polyesters of tetrahydrophthalic anhydride at least one additionaldiacid (or corresponding acid halide or anhydride) and one or morealiphatic diols; and polyesters of 1,4-dihydroxy-but-2-ene with one ormore diacids (or corresponding acid halides or anhydrides).

Starting polymer type iv) is an allyl ester of a novolac resin. By“novolac” resin, it is meant a polymer of formaldehyde and a phenoliccompound such as phenol or cresol. The phenolic compound optionally maycontain 1 or 2 substituent groups on the ring (which may includebromine). Preferably, the phenolic compound contains no such substituentor only one substituent group, especially lower alkyl such as methyl, inthe para-position. Starting polymers of type (iv) include thoserepresented by the idealized structure:

wherein R⁵ represents a substituent group, such as alkyl or othersubstitution, and m is from 0 to 3. These polymers can be prepared froma novolac resin, many of which are commercially available. Allyl ethergroups can be introduced by reaction of a phenolic hydroxyl group withsodium hydride to form alkoxide groups, which then react with an allylhalide such as allyl chloride or allyl bromide to produce the ether.

ROMP polymers (starting polymer type v) are homopolymers or copolymersthat are formed in a ring-opening metathesis polymerization (ROMP)process from certain non-aromatic cyclic monomers that havecarbon-carbon unsaturation in a ring structure. Examples of ROMPpolymers that are useful as starting materials include homopolymers andcopolymers of cyclopentene, cyclooctene, norbornene,cyclohexenylnorbornene, exo-norbornene dicarboxylic anhydride anddicyclopentadiene. Examples of suitable comonomers include cyclicolefins such as cyclooctene. The ROMP polymers and copolymers containcarbon-carbon double bonds in the main polymer chain.

Starting polymers of type (vi) as well as methods for brominating thesepolymers are described in WO 2007/019120.

The aliphatic bromine-containing polymer can be prepared from any of theaforementioned starting polymers or other polymers that containaliphatic carbon-carbon unsaturation by adding bromine across thealiphatic carbon-carbon unsaturation. The bromination may be performedusing a direct bromination process, in which e.g., the startingbutadiene polymer is brominated with elemental bromine as described inWO 2008/021418. An aliphatic alcohol may be present during thebromination reaction, also as described in WO 2008/021418. Residualbromine and other by-products can be removed from the resultingaliphatic bromine-containing polymer solution, by extraction, washing,or other useful methods.

Alternatively, the aliphatic bromine-containing polymer may be obtainedby brominating the starting polymer with a quaternary ammoniumtribromide as described, for example, in WO 2008/021417. In a preferredsuch process, the starting polymer is contacted with the quaternaryammonium tribromide under conditions such that they react to produce asolution of the aliphatic bromine-containing polymer and a quaternaryammonium monobromide byproduct. The quaternary ammonium monobromide ispreferably extracted with an aqueous phase containing a reducing agentto remove the quaternary ammonium monobromide stream from the brominatedpolymer.

It is preferred to brominate at least 60, 70, 75, 80 or 85% of thealiphatic carbon-carbon unsaturation sites contained in the startingpolymer. Generally, higher bromination rates are preferred, as thisreduces the number of residual sites of aliphatic carbon-carbonunsaturation in the polymer, and thus reduces the chances of gelformation when the aliphatic bromine-containing polymer undergoesthermal processing. Therefore, it is more preferred to brominate atleast 90% or at least 95% of the sites of aliphatic carbon-carbonunsaturation. Up to 100% of the aliphatic carbon-carbon unsaturationsites may be brominated. A practical upper limit is generally up to 98%or up to 99%.

The aliphatic bromine-containing polymer is useful as an FR additive fora bulk polymer. Preferably, enough of the aliphatic bromine-containingpolymer is present in a blend with the bulk polymer to provide the blendwith a bromine content within a range of from 0.1 percent by weight to25 percent by weight, based upon blend weight. A preferred bromineconcentration in the blend (provided by the FR additive) is from 0.25 to10 percent by weight, a more preferred amount is from 0.5 to 5 weightpercent, and a still more preferred amount is from 1 to 3 weightpercent. The amount of aliphatic bromine-containing polymer that isneeded to provide a given bromine content to the blend will of coursedepend on its bromine content. In general, however, as little as about0.15 parts by weight of the aliphatic bromine-containing polymer can beprovided per 100 parts by weight bulk resin (pphr). At least 0.4 pphr orat least 0.8 pphr of the aliphatic bromine-containing polymer can beprovided. Up to 100 pphr of the aliphatic bromine-containing polymer canbe present in the blend, but a more preferred maximum amount is 50 pphr,a more preferred maximum amount is 20 pphr and a still more preferredmaximum amount is 10 pphr or even 7.5 pphr.

In some embodiments, the blend contains at least one alkyl phosphitecompound. Suitable alkyl phosphites are described in “Plastic AdditiveHandbook”, edited by H. Zweifel, 5^(th) Ed., p. 441 (2001). The alkylphosphite compound contains at least one

group, in which each R group is an unsubstituted or substituted alkylgroup. The two R groups together may form a divalent group, which may besubstituted, that bonds to the adjacent —O— atoms through an aliphaticcarbon to form a ring structure that includes the —O—P—O— linkage. The Rgroups may be linear or branched. The carbon atom on the R groups thatis adjacent to and bonded to the —O— atom is preferably a methylene(—CH₂—) carbon. Substituent groups on the R groups may be, for example,aryl, cycloalkyl,

or an inert substituent. The R¹ group in the foregoing structures may beanother R group, or an aryl or substituted aryl group.

A preferred type of R¹ group is an aryl group that is substituted withat least one branched alkyl group that contains a tertiary carbon atom.The branched alkyl group that contains a tertiary carbon atom may befurther substituted with one or more aryl groups. Another preferred typeof R¹ group is an alkyl group, which may be branched or linear, havingfrom 2 to 30, preferably from 8 to 20, carbon atoms. Examples ofsuitable R¹ groups include dodecyl, tetradecyl, hexadecyl, octadecyl,2,4-di-(t-butyl)-phenyl,

A preferred alkyl phosphite is a pentaerythritol diphosphite compound.These materials have the structure

wherein R² is an unsubstituted or substituted, linear or branched, alkylgroup, an aryl group or a substituted aryl group.

Specific examples of preferred alkyl phosphites include bis(2,4-dicumylphenyl)pentaerythritol diphosphite, distearylpentaerythritoldiphosphite and di (2,4-di-(t-butyl)phenyl)pentaerythritol diphosphite.These are commercially available as Doverphos™ S-9228 (Dover ChemicalCorporation), Doverphos™ S-682 (Dover Chemical Corporation) and Irgafos™126 (Ciba Specialty Chemicals).

The alkyl phosphite compound preferably is soluble in the aliphaticbromine-containing polymer to the extent of at least 10, preferably atleast 20, and more preferably to at least 40, parts of alkyl phosphitecompound per 100 parts by weight of the aliphatic bromine-containingpolymer.

The alkyl phosphite compound is suitably present (if used) in an amountof from about 1 to about 40 parts, preferably from about 1 to about 30parts and more preferably from about 1 to about 20 parts by weight per100 parts by weight of the aliphatic bromine-containing compound. Ablend of an alkyl phosphite with the aliphatic bromine-containingcompound and the bulk polymer will generally contain at least 0.0015,preferably at least 0.0025, more preferably at least 0.005 and stillmore preferably 0.01 parts by weight of the alkyl phosphite per 100parts by weight of the bulk polymer (pphr). Such a blend may contain asmuch as 40 pphr of the alkyl phosphite compound, but preferably thealkyl phosphite is not present in an amount greater than 20 pphr, morepreferably not greater than 8 pphr, still more preferably not greaterthan 4 pphr and even more preferably not greater than 2 pphr.

In other embodiments, an epoxy compound is present in the blend. Theepoxy compound contains on average at least one and preferably two ormore epoxide groups per molecule. The epoxy compound preferably has anequivalent weight per epoxide group of no more than 2000, preferably nomore than 1000 and even more preferably no more than 500. The molecularweight of the epoxy compound is at least 1000 in preferred embodiments.The epoxy compound may be brominated. A variety of commerciallyavailable epoxy resins are suitable. These may be based, for example, ona bisphenol compound, such as various diglycidyl ethers of bisphenol A.They may be based on a brominated bisphenol compound. The epoxy compoundmay be an epoxy novolac resin, or an epoxy cresol novolac resin. Theepoxy compound may be an entirely aliphatic material, such as adiglycidyl ether of a polyether diol or an epoxidized vegetable oil.Examples of commercially available epoxy compounds that are usefulherein include F2200HM and F2001 (from ICL Industrial Products), DEN 439(from The Dow Chemical Company), Araldite ECN-1273 and ECN-1280 (fromHuntsman Advanced Materials Americas, Inc.), and Plaschek 775 (fromFerro Chemical Co.).

The epoxy compound is suitably present (if used) in an amount of fromabout 1 to about 40, preferably from about 1 to about 20 parts by weightper 100 parts by weight of the aliphatic bromine-containing compound. Ablend of an epoxy compound with the aliphatic bromine-containingcompound and the bulk polymer will generally contain at least 0.0015,preferably at least 0.0025, more preferably at least 0.005 and stillmore preferably 0.01 parts by weight of the epoxy compound per 100 partsby weight of the bulk polymer (pphr). Such a blend may contain as muchas 40 pphr of the epoxy compound, but preferably the epoxy compound isnot present in an amount greater than 20 pphr, more preferably notgreater than 8 pphr, still more preferably not greater than 4 pphr andeven more preferably not greater than 2 pphr.

It is preferred that both the alkyl phosphite and the epoxy compound arepresent in the blend. In such a case, the alkyl phosphite compound andthe epoxy compound are each present in an amount of from 1 to 40 or from1 to 20 parts by weight per 100 parts by weight of the aliphaticbromine-containing polymer. The blend in such cases preferably containsfrom 0.0015 to 20, especially from 0.005 to 2 pphr of the epoxy compoundand from 0.0015 to 20, preferably from 0.005 to 2 pphr, and morepreferably from 0.01 to 1.2 pphr of the alkyl phosphite compound.

Other stabilizers and/or acid scavengers can be present, in addition tothe alkyl phosphite and the epoxy compound. Examples of such materialsinclude, for example, inorganic materials such as tetrasodiumpyrophosphate, hydrocalumite, hydrotalcite and hydrotalcite-like clays;polyhydroxyl compounds having a molecular weight of 1000 or below, suchas pentaerythritol, dipentaerythritol, glycerol, xylitol, sorbitol ormannitol, or partial esters thereof; and organotin stabilizers which maybe allylophilic and/or dieneophilic. The organotin compounds include,for example, alkyl tin thioglycolates, alkyl tin mercaptopropionates,alkyl tin mercaptides, alkyl tin maleates and alkyl tin (alkylmaleates),wherein the alkyls are selected from methyl, butyl and octyl. Suitableorganotin compounds are available commercially from Ferro Corporation(i.e., Thermchek™ 832, Thermchek™ 835), and Baerlocher GmbH (i.e.,Baerostab™ OM 36, Baerostab™ M25, Baerstab™ MSO, Baerostab™ M63,Baerostab™ OM 710S).

It is generally preferable to use no greater than about 0.5 pphr, in theaggregate, of such inorganic materials, polyhydroxyl compound andorganotin stabilizers, as these materials tend to plasticize the polymerand/or interfere with cell structure if used in too great a quantity. Inparticular, the amount of organotin stabilizer is preferably no greaterthan 0.5 pphr, and if present, preferably is present at a level of from0.1 to 0.4 pphr. In some embodiments, these materials are absent fromthe composition.

A mixture of the bulk polymer and the aliphatic bromine-containingpolymer is melt processed in the presence of the alkyl phosphite and/orthe epoxy compound. Other, optional ingredients may be present asnecessary or desired for the particular melt processing operation.

Melt processing, for purposes of this invention, involves creating amelt of the bulk polymer and the aliphatic bromine-containing polymer,forming the melt, and then cooling the melt to solidify it and form anarticle. Various melt processing operations are within the scope of thisinvention, such as extrusion, injection molding, compression molding,casting, and the like. The melt processing operation of most interest isextrusion foaming. In each case, the melt processing operation can beconducted in any convenient manner. Apart from the presence of thealiphatic bromine-containing polymer, alkyl phosphite and/or epoxycompound, the melt processing operations may be entirely conventional.

Other additives which may be present during the melt processingoperation include, for example, lubricants such as barium stearate orzinc stearate; UV stabilizers, pigments, nucleating agents,plasticizers, FR synergists, IR blockers, and the like.

Extrusion foaming is performed by forming a pressurized melt thatcontains the bulk polymer, the aliphatic bromine-containing polymer, ablowing agent, the alkyl phosphite and/or the epoxy compound and otheradditives such as may be useful. Once the raw materials have been mixedand the polymers melted, the resulting gel is forced through an openinginto a zone of lower pressure, where the blowing agent expands and thepolymer solidifies to form a foam. The extruded foam can take the formof a sheet (having a thickness of up to inch (12 mm)), plank orboardstock (having a thickness of from inch (12 mm) to 12 inches (30 cm)or more), or other convenient shape. The foam can be extruded to formcoalesced strand foam if desired.

The various raw materials can be fed into the processing equipmentindividually, or in various combinations. The alkyl phosphite and/orepoxy resin can be preblended with, for example, the aliphaticbromine-containing polymer, the bulk polymer, or both. Similarly, thealiphatic bromine-containing polymer can be introduced as a separatecomponent, or premixed in some way with the bulk polymer. A premix canbe in the form of a dry blend of particles of the bulk polymer andparticles of the aliphatic bromine-containing polymer. Alternatively, orin addition, the bulk polymer and aliphatic bromine-containing polymercan be melt-blended prior to the melt processing operation, and themolten mixture or particles of the blend can be introduced into the meltprocessing operation. It is generally preferred to introduce the blowingagent as a separate stream after the polymeric materials have beenmelted.

The blowing agent in an extrusion foaming process can be an exothermic(chemical) type or an endothermic (physical) type. Physical blowingagents such as carbon dioxide, various hydrocarbons, hydrofluorocarbons,water, alcohols, ethers and hydrochlorofluorocarbons are especiallysuitable.

Melt processing operations tend to produce a certain amount of scrapmaterial. This is especially true for extrusion foaming operations, dueto the production of out-of-specification foam, especially duringstartups and process upsets, and because a certain amount of fabricationis often performed after the foam is made. When possible, it is desiredto recycle the scrap material back into the process to reduce rawmaterial losses and so improve process economics. However, the scrapmaterial cannot be recycled if it contains significant amounts of gels,or if it forms significant amount of gels when it is recycled throughthe process.

Gels are masses of polymeric material which, due to crosslinking, are nolonger thermoplastic and are not evenly dispersible or deformable in themolten bulk polymer or the aliphatic bromine-containing polymer. Thealiphatic bromine-containing polymer is somewhat susceptible to gelformation, mainly because it may contain residual aliphaticcarbon-carbon double bonds, or/and can eliminate HBr during the meltprocessing operation to generate aliphatic carbon-carbon double bonds.The carbon-carbon double bonds represent sites which can engage incrosslinking reactions to form higher molecular weight species and gels.

When scrap is recycled through the process, specific molecules of thealiphatic bromine-containing polymer can pass through the meltprocessing operation multiple times. The more times an aliphaticbromine-containing polymer passes through the melt processing step, thegreater chance it has to crosslink and form gels.

An advantage of this invention is that the alkyl phosphite and the epoxycompound are each effective in preventing the aliphaticbromine-containing polymer from forming gels during melt processing. Thecombination of the alkyl phosphite and the epoxy compound generallyperforms especially well. This greatly facilitates the use of thealiphatic bromine-containing polymer in melt processing operations,notably extrusion foaming operations, in which scrap material from theprocess is recycled through the melt processing operation.

The article produced in the melt processing operation can be used in thesame manner as similar articles made in other melt processingoperations. When the article is a foam, the foam preferably has adensity of up to 80 kg/m³, more preferably up to 64 kg/m³ and even morepreferably up to 48 kg/m³. Foam that is used as thermal insulation ispreferably in the form of boardstock having a density of from 24 to 48kg/m³. Billet foam preferably has a density of from 24 to 64 kg/m³, morepreferably from 28 to 48 kg/m³. The foams preferably have an averagecell size in the range of from 0.1 mm to 4.0 mm, especially from 0.1 to0.8 mm, per ASTM D3576. The foam may be predominantly closed-celled,i.e., may contain 30% or less, preferably 10% or less and even morepreferably 5% or less of open cells, per ASTM D6226-05. More open-celledfoams also may be produced in accordance with the invention.

Boardstock foams made in accordance with the invention are useful asbuilding foam insulation, as part of roof or wall assemblies. Otherfoams made in accordance with the invention can be used as decorativebillet, pipe insulation and in molded concrete foundation applications.

The following examples are provided to illustrate the invention, but notto limit the scope thereof. All parts and percentages are by weightunless otherwise indicated.

EXAMPLES 1-4

Screen experiments are done to evaluate the ability of variousstabilizers to prevent thermally-induced gelling in a brominatedbutadiene polymer. The brominated butadiene polymer in the screeningexperiments is a styrene/butadiene/styrene triblock polymer containing60% by weight butadiene prior to bromination. This starting polymer isbrominated using elemental bromine as the brominating agent as describedin WO2008/021418, and the resulting brominated material has a brominecontent of 62% by weight. Three percent of the aliphatic carbon-carbondouble bonds in the starting polymer remain after the bromination. 3.5%of the carbon-bromine C—Br bonds are to allylic or tertiary carbonatoms, which are less thermally stable than the other C—Br bonds in thestructure.

In each screening experiment, the brominated butadiene is melt-blendedwith a stabilizer in the amount shown in Table 1 below. The blendedmaterial is ground in a mortar and pestle and then is immersed inmethylene chloride at a proportion of 1 g of the blend per 10 mL ofmethylene chloride. A film of this blend is cast and dried in a vacuumoven at 30° C. The film sample in each case is equilibrated at 30° C.under nitrogen for 5 minutes, and then heated to 180° C. under nitrogenat the rate of 20° C./minute on a thermogravimetric analyzer (TGA). Thesamples are maintained at 180° C. for 20 minutes and then cooled to 30°C. at the rate of 50° C./minute, all under nitrogen. The sample is thenplaced in 2 mL of methylene chloride and inspected visually to determinewhether the brominated butadiene polymer dissolves. The presence ofundissolved and/or gelled material indicates that cross-linking hasoccurred under the conditions of the heating regimen, and so indicatesthe effectiveness of the various stabilizers tested to preventthermally-induced crosslinking.

In addition, the 5% weight loss temperature of the heat-treated productis evaluated using thermogravimetric analysis. 10 milligrams of thepolymer blend is analyzed using a TA Instruments model Hi-Res TGA 2950or equivalent device, with a 60 milliliters per minute (mL/min) flow ofgaseous nitrogen and a heating rate of 10° C./min over a range of fromroom temperature (nominally 25° C.) to 600° C. The mass lost by thesample is monitored during the heating step, and the temperature atwhich the sample has lost 5% of its weight at 100° C. (after i.e., aftervolatiles have been driven off) is designated the 5% weight losstemperature (5% WLT).

The various stabilizers that are evaluated, the amount of stabilizerused in each case, the solubility after thermal aging and the 5% WLT areas reported in Table 1.

TABLE 1 Amount, Soluble parts/100 parts after Stabilizer type resin 5%WLT Aging? None 0 195 No di-(2,4-di-(t-butyl)phenyl) 4 243 Yespentaerythritol diphosphite¹ distearylpentaerythritol 8 241 Yesdiphosphite² (2,4-dicumylphenyl) 8 246 Yes pentaerythritol diphosphite³Epoxy cresol novolac resin 14 237 No Epoxidized soybean oil 14 218 NoBrominated epoxy resin 14 225 No Ester-modified sulfide⁴ 8 210 NoCommercial antioxidant A⁵ 8 ND No Commerial antioxidant B⁶ 8 195 NoCommercial antioxidant C⁷ 8 207 No Commercial Antioxidant D⁸ 8 200 NoCommercial organotin stabilizer 8 226 No A⁹ Dioctyl tin maleate 8 233 NoBHT 8 ND No Commercial organotin stabilizer 8 ND No B¹⁰ Tris(2,4-di-tert- 8 202 No butylphenyl)phosphite ¹Irganox ™ 126, from Ciba,CAS No. 26741-53-7. ²Doverphos ™ S682, from Dover Chemical Corporation.³Doverphos ™ S9228 from Dover Chemical Corporation. ⁴Irganox ™ PS800FL8,from Ciba, CAS No. 123, 28-4. ⁵Irganox ™ 38, from Ciba, CAS No.145650-60-8. ⁶Irganox ™565, from Ciba, CAS No. 991-84-4. ⁷Irganox ™1076,from Ciba, CAS No. 2082-79-3. ⁸Irganox ™B215, from Ciba.⁹Baerostab ™0M36, from Baerolocher GmbH. ¹⁰Thermchek 835 from FerroCorporation.

On the basis of the screening experiments, di-(2,4-di-(t-butyl)phenyl)pentaerythritol diphosphite, distearylpentaerythritol diphosphite and(2,4-dicumylphenyl) pentaerythritol diphosphite are identified asmaterials which provide both good suppression of crosslinking in thebrominated butadiene polymer as well as a significant increase in 5%WLT.

A blend of 50 grams of a commercial foam-grade polystyrene resin, 1.5grams of the same brominated styrene/butadiene/styrene block copolymerand 0.25 grams of an epoxy cresol novolac resin is made as follows. Thepolystyrene resin is charged to a Haake Rheocord™ 90 with controller andmixing bowl containing roller blade mixers. The bowl is preheated to180° C. The polystyrene is blended for 2 minutes at 40 rpm, and then thebrominated copolymer and epoxy resin are added as a dry blend. Blendingis continued for another 8 minutes at the same temperature and speed.The resulting blend is designated Example 1.

Examples 2-7 and Comparative Sample A are made in the same manner byvarying the stabilizer package in each case. The stabilizer package ineach case is as indicated in Table 2 below. Comparative Sample Acontains no stabilizer package.

The amount of the brominated block copolymer that remains soluble (andthus ungelled) in each of Examples 1-7 and Comparative Sample A isestimated in the following manner. The sample is in each case dissolvedin toluene and filtered, and bromine content in the both the originalunfiltered and filtered solutions is determined by x-ray fluorescence,using a bench-top energy dispersive x-ray spectrometer. Calibrationstandards are prepared from pure samples of the brominated butadienepolymer, using the Compton peak correction method. The ratio of thesemeasured bromine contents correlates to the percentage of cross-linkedbrominated butadiene polymer. The estimates in each case are as reportedin Table 2. In each case, the margin of error is believed to be ±5percentage points.

A portion of each blend is separately heated to 230° C. on athermogravimetric analyzer, and held at that temperature. The time atwhich the sample exhibits a measurable weight loss is determined as anindication of the thermal stability of the blend. Results are asreported in Table 2.

TABLE 2 di-(2,4-di-(t- butyl)phenyl) Example or Dioctyltinpentaerythritol Epoxy cresol % Soluble Comparative maleate, diphosphite,novolac Brominated Block 230° C. Onset Sample No. pphr pphr resin, pphrCopolymer¹ Time, min.² A* 0 0 0 30 5.7 1 0 0 0.5 48 9.7 2 0 0 1.0 5916.8 3 0 0.2 0.5 61 16.1 4 0 0.4 0.5 63 17.3 5 0.2 0 0.5 54 15.9 6 0.20.2 0.5 43 19.9 7 0.4 0.2 0.5 42 19.2 ¹The weight percent of thebrominated butadiene block copolymer that remains ungelled aftertreatment at 180° C. in the Haake blender. ²The amount of time at 230°C. before the blend shows evidence of degradation (as weight loss). *Notan example of this invention.

The brominated butadiene copolymer used in this set of experimentscontains a somewhat high level of bromine weakly bonded to allylic ortertiary carbons. With no stabilizer package present (Comparative SampleA), the copolymer gels very significantly and begins to show thermaldegradation after less than 6 minutes at 230° C. Adding an epoxy resinalone, as in Examples 1 and 2, reduces gelling and provides greaterthermal stability. However, one weight percent of the epoxy resin (as inExample 2) is a somewhat high level, as the epoxy can plasticize thepolystyrene when present at such a level. Accordingly, it is desired toreduce the epoxy resin loading and maintain equivalent or betterresults.

Example 3 shows the effect of replacing half of the epoxy resin used inExample 2 with 0.2% of the alkyl phosphite. Gelling is comparable inthese two cases, and only a small loss of thermal stability is seen onthe 230° C. thermal aging test.

Example 4 shows that by increasing the alkyl phosphite level to 0.4%,gelling is reduced significantly and the blend is slightly morethermally stable. Total additive level remains below that of Example 2.

Examples 5, 6 and 7 show the effect of adding a small amount of anorganotin stabilizer to the blends of Examples 1 and 3. Thermalstability is improved significantly in each case. Less of the brominatedbutadiene remains soluble than in Examples 1 or 3, but this may be dueto a change in solubility parameter caused by the presence of theorganotin stabilizer, rather than an actual reduction in effectivenessof the stabilizer package. At the 0.4% level, the organotin stabilizercan begin to interfere with the cell structure of a polystyrene foam.

EXAMPLES 8-17 AND COMPARATIVE SAMPLE B

Examples 8-17 and Comparative Sample B are made in the same manner asthe previous examples. The brominated butadiene polymer in this case isa styrene/butadiene/styrene triblock polymer containing 60% by weightbutadiene prior to bromination. This starting polymer is brominatedusing a quaternary ammonium bromide as the brominating agent asdescribed in WO2008021417. The resulting brominated material has abromine content of 63%. The brominated butadiene polymer contains 7%residual aliphatic carbon-carbon double bonds. Fewer than 1% of thecarbon-bromine bonds in this brominated polymer are at allylic ortertiary carbon atoms. The antioxidant packages used in this set ofexperiments are as indicated in Table 3. The amount of solublebrominated butadiene polymer in each blend and the 230° C. onset timefor each blend are determined as described in the previous examples.Results are as indicated in Table 3.

TABLE 3 di-(2,4-di-(t- (2,4- Epoxy Ex. or butyl)phenyl) dicumylphenyl)Distearyl cresol % Soluble 230° C. Comp. pentaerythritol pentaerythritolpentaerythritol novolac Brominated Onset Samp. diphosphite, diphosphite,diphosphite, resin, Block Time, No. pphr pphr pphr pphr Copolymer¹ min.²B* 0 0 0 0 58 7 8 0 0 0 0.5 87 10 9 0.4 0 0 0 83 10 10 0.8 0 0 0 90 1111 0.4 0 0 0.5 89 22 12 0 0.4 0 0 84 11 13 0 0.8 0 0 88 11 14 0 0.4 00.5 91 27 15 0 0 0.4 0 88 12 16 0 0 0.8 0 89 11 17 0 0 0.4 0.5 88 22*Not an example of the invention.

The data in Table 3 shows that each of di-(2,4-di-(t-butyl)phenyl)pentaerythritol diphosphite, (2,4-dicumylphenyl) pentaerythritoldiphosphite, distearyl pentaerythritol diphosphite and the epoxy cresolnovolac resin are effective in reducing gellation of the brominatedbutadiene polymer and in retarding the degradation of the brominatedbutadiene polymer. However, increasing the levels of the phosphites from0.4 to 0.8 pphr has little additional beneficial effect. When the alkylphosphite and epoxy cresol novolac resin are used together (as inExamples 11, 14 and 17), a very significant lengthening of the 230° C.onset time is seen.

1. A polymer composition comprising (a) a bulk polymer, (b) an aliphaticbromine-containing polymer, and (c) a mixture of at least one alkylphosphite and at least one epoxy compound.
 2. The polymer composition ofclaim 1, wherein from 1 to 40 parts by weight of the epoxy compound arepresent per 100 parts by weight of the aliphatic bromine-containingpolymer.
 3. The polymer composition of claim 1, wherein from 1 to 40parts by weight of the alkyl phosphite are present per 100 parts byweight of the aliphatic bromine-containing polymer.
 4. The polymercomposition of claim 1, wherein the aliphatic bromine-containing polymeris a brominated butadiene homopolymer or a brominated styrene/butadieneblock copolymer.
 5. The polymer composition of claim 1 wherein thealiphatic bromine-containing polymer is a copolymer of styrene andallylmaleimide; an aliphatically unsaturated polyester; an allyl etherof a novolac novolac resin, or a ROMP polymer or copolymer.
 6. Thepolymer composition of claim 1 wherein the bulk polymer is a polymer orcopolymer of styrene.
 7. The polymer composition of claim 2, which is inthe form of a foam.
 8. The polymer composition of claim 1, wherein thealkyl phosphite contains at least one

moiety, in which each R group is an unsubstituted or substituted, linearor branched, alkyl group, or the two R groups together form a divalentgroup, which may be substituted, that bonds to the adjacent —O— atomsthrough an aliphatic carbon to form a ring structure that includes a—O—P—O— linkage, and the R¹ group is another R group, or an aryl orsubstituted aryl group.
 9. The polymer composition of claim 1, whereinthe alkyl phosphite is a pentaerythritol diphosphite compound having thestructure

wherein each R² is an unsubstituted or substituted, linear or branched,alkyl group, an aryl group or a substituted aryl group.
 10. The polymercomposition of claim 9, wherein the alkyl phosphite is bis(2,4-dicumylphenyl)pentaerythritol diphosphite, distearylpentaerythritoldiphosphite or di(2,4-di-(t-butyl)phenyl)pentaerythritol diphosphite.11. A method for producing a polymer composition of claim 1, comprisingmelt processing a mixture containing a molten bulk polymer and analiphatic bromine-containing polymer or copolymer in the presence of amixture of at least one alkyl phosphite and at least one epoxy compound.12-15. (canceled)